It is estimated that up to 43 million Americans have a disabling condition that limits one or more of their daily activities, and that 38% of people with disabilities have significant mobility limitations. Biomechanically-based movement analysis is used increasingly in the surgical and medical treatment of a variety of neuromuscular and musculoskeletal disorders associated with these functional limitations. Inverse dynamics analysis provides data on the joint kinetics -- net muscle moments and powers used at joints during movement -- which reveal the neuromuscular strategies used to produce the observed movement. A patient's gait patterns are often evaluated using comparisons with data obtained from healthy individuals, despite the fact that many patients walk at much slower speeds. It is important when interpreting a patient's data to distinguish which variations from normal are due solely to differences in walking speed and which are due to neuromuscular abnormalities or adaptations other than speed. The purpose of this project is to investigate the effect of dramatically different walking speeds on the mechanics of gait, as well as the effect of measurement variation on the interpretation of gait data.